Optical assembly

ABSTRACT

An optical assembly has a number of optical fibers which terminate at connectors which connect to short lengths of optical fibers which connect, in turn, to an optical back plane mounted within a housing. The connectors are withdrawn from the housing for inspection. A plurality of movable guides is provided for the short fibers to determine a number of optical paths which remain of constant length as the connectors are withdrawn from the housing.

BACKGROUND OF THE INVENTION

This invention relates to an optical assembly, and is concerned with themounting of terminations of optical fibres in a manner which permitstheir visual inspection. Optical fibres are used for the transmission ofdata and telecommunications and the like, and a large number ofindividual optical fibres are required to be terminated in equipmentassociated with a switch or other node at which the optical informationis to be processed, eg by way of routing to its destination, combiningwith other information in a multiplex fashion or by switchinginformation from one optical carrier wavelength to another.

The optical connections are housed within an enclosure, and in practicemany such optical connections may need to be housed within a commonenclosure. In the event of a fault in the optical system, or for regularmaintenance, it is highly desirable to locate the optical connections ina manner which facilitates their inspection and checking. This isdifficult if the optical connections are mounted within an equipmentenclosure, such as a large cabinet or rack.

The present invention seeks to provide an improved optical assembly.

SUMMARY OF THE INVENTION

According to this invention an optical assembly includes a plurality ofoptical connectors mounted in a fixed physical relationship with eachother; a housing within which the connectors are normally housed andfrom which they can be withdrawn to permit inspection; a plurality ofoptical fibres each terminating at a respective one of the opticalconnectors; and a plurality of movable guides which determine aplurality of optical paths, each of the same path length, for theoptical fibres, the guides being of fixed spacing and orientationrelative to each other and being movable both with respect to saidconnectors and said housing so as to maintain said path lengthsubstantially constant as the connectors are withdrawn from saidhousing.

Preferably the plurality of movable guides are movable along a curvedline as the connectors are withdrawn from said housing, the line beingcurved so as to maintain said path length substantially constant.

Preferably again the line is curved so as to approximate an arc of aparabola. Over a sufficiently short arc of a parabola having a shallowcurvature, the arc approximates to that of a circle. In practice, an arcof constant radius is satisfactory provided that the length of the arcis short in relation to the radius.

The invention is further described by way of example with reference tothe accompanying drawings, in which:

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an optical assembly in accordance with the invention,in which optical connectors are located within a housing, and

FIG. 2 illustrates the optical assembly in which the optical connectorsare shown in their withdrawn position.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to FIG. 1, there is shown therein an optical assembly formingpart of communications equipment and consisting of a housing 1, having afront surface 2 carrying eight optical connectors 3, a back surfacewhich defines an optical back plane 4, two end faces 5, 6, and top andbottom surfaces (not shown). If the assembly forms part of a largerequipment, some of these surfaces can be omitted.

Information such as data or telephony is carried to or from eachconnector 3 via optical fibres 7. Each fibre 7 will link to othercommunications equipment, and in practice, these fibres 7 may be manykilometres in length. The fibres 7 terminate at the connectors 3 whichare mounted in readily accessible positions at the front of the housing.The optical back plane 4 includes electro-optical components oroptical-optical components which permit optical signals to be processedby way of switching, multiplexing or the like, and fibres 11-18 areprovided linking each of the connectors 3 to the optical back plane 4.Although each fibre 11-18 may be a short length of fibre opticallycoupled to the optical back plane 4 by means of additional opticalconnectors (not shown), typically the ends of the fibres 11-18 remotefrom the connectors 3 form an integral part of the optical back plane 4where they are routed as necessary and terminated at the appropriateoptical component. Because fibres 11-18 form an integral attachment withthe optical back plane, replacement of a fibre would be an expensive anddifficult process.

A plate 19 is fixed to the front surface 2, and it supports a first setof eight curved guides 20 which are fixed to the plate 19. The plate 19is provided with two curved slots 21, 22 in which are mounted respectivepegs 23 and 24 which are attached to a further plate 25 which carries asecond set of eight further curved guides 26. The pegs 23 and 24 areslidable along respective slots 21, 22.

A third set of curved guides 27 is mounted in a fixed relationship withthe housing 1, and hence the back plane 4. A pair of rigid arms 28, 29link the pegs 23, 24 to pivotally mounted attachment points 30, 31 onthe housing 1.

The three sets of curved guides define optical paths for each of thefibres 11-18 from the connectors 3 on the front surface 2 to the opticalback plane 4.

To permit visual inspection of each optical connector 3, the frontsurface 2 on which they are mounted can be withdrawn from the housing 1.The plate 19 which is attached to the front surface 2 is slidablymounted in the housing, so that the plate 19 can be partially withdrawn,as shown in FIG. 2. The connectors 3 are now clear of the housing 1, andso can easily be checked and inspected for faults.

Clearly, the guides 20 which are mounted on the plate 19 move with thefront surface 2 and the connectors 3 when they are withdrawn from thehousing.

From FIG. 2, it can be seen that as the connectors 3 are withdrawn fromthe housing 1, the pegs 23 and 24 are constrained by the pivotallymounted arms 28, 29 to slide along the slots 21, 22 and to thereby movethe second set of guides 26, so as to alter the paths of the opticalfibres 11-18.

The slots 21, 22 are so curved as to ensure that the path lengths of theoptical fibres remain substantially constant as the connectors 3, andthe plate 19 are withdrawn from the housing 2.

The slots 21, 22 take the form of a short arc of a parabolic curve, butas the slots are short they approximate to an arc of a circle of largeradius.

It will be understood that the second set of guides 26 move relative toboth the first and third sets of guides, the position of the second setbeing determined by the slots 21, 22 and by the arms 28, 29. Byselecting the lengths of the arms 28 and 29 in relation to the shape ofthe slots 21 and 22, the fibre paths of substantially constant lengthcan be achieved. This is important as the optical fibres are fragile andeasily damaged, but are expensive to replace.

What is claimed is:
 1. An optical assembly, comprising; a) a pluralityof optical connectors mounted in a fixed physical relationship with eachother; b) a housing within which the connectors are normally housed andfrom which the connectors are withdrawn to permit inspection; c) aplurality of optical fibers each terminating at a respective one of theconnectors; and d) a plurality of movable guides for determining aplurality of optical paths, each path having the same path length forthe optical fibers, the guides being of fixed spacing and orientationrelative to each other, and the guides being movable both with respectto the connectors and to the housing so as to maintain said path lengthsubstantially constant as the connectors are withdrawn from the housing.2. The optical assembly as claimed in claim 1, wherein the plurality ofmovable guides is movable along a curved line as the connectors arewithdrawn from the housing, the curved line serving to maintain saidpath length substantially constant.
 3. The optical assembly as claimedin claim 2, wherein the curved line is a parabolic arc.
 4. The opticalassembly as claimed in claim 2, wherein the curved line is a circulararc.
 5. The optical assembly as claimed in claim 2, wherein theplurality of guides is mounted on a common plate which is attached tothe housing by a plurality of pivotally mounted arms.
 6. The opticalassembly as claimed in claim 5, wherein the plurality of opticalconnectors is mounted in fixed relationship with the common plate,wherein the plate has two slots, each slot defining the curved line, andwherein the arms have ends attached to the plate and slidable along theslots.
 7. The optical assembly as claimed in claim 6, wherein a firstset of the guides is mounted adjacent to the connectors in a fixedposition therewith so as to define a part of the optical paths.
 8. Theoptical assembly as claimed in claim 7, wherein the plurality of movableguides constitutes a second set of guides positioned between the firstset and a third set of guides which is mounted in a fixed positionrelative to the housing, and wherein the first, second and third setsdefine said optical paths.